‘Specialized’ Microbes Within Plant Species Promote Diversity, Study Finds

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It’s widely accepted within agriculture that maintaining genetic diversity is important. In areas where crop plants are more diverse, pathogens might kill some plants but are less likely to wipe out an entire crop.

Few studies, however, have focused on such highly specialized pathogens in natural plant communities. In diverse plant communities, pathogens are thought to maintain diversity by killing common species, making room for rare ones. But what happens to diversity if, like in agriculture, pathogens harm some plants within a species, but not all?

A Yale)-led research team has found that tree seedlings grew less effectively in soil located below their mother tree than in soil found under a different individual of the same species. After ruling out other potential drivers, they concluded that the differences in growth were most likely due to microbial pathogens that specialize at the genotype level. Theoretical models revealed that such highly specialized pathogens could help maintain diversity in tree communities and promote increased seed dispersal over evolutionary timescales.

“We often think of pathogens as pests,” said Jenalle Eck, a postdoctoral researcher at the University of Zurich and a former visiting doctoral student at the Yale School of Forestry & Environmental Studies (F&ES), “but we’re finding that they play a key role in a highly diverse ecosystem.”

The study was published in the Proceedings of the National Academy of Sciences. The senior author of the paper was Liza Comita, an assistant professor of tropical forest ecology at F&ES.

For the study, Eck conducted a shadehouse experiment, potting more than 200 seedlings of the tropical tree Virola surinamensis grown from seeds collected in a diverse tropical forest in Panama. The soil for the pots was sourced from either the seedlings’ maternal tree or other trees of the same species.

The researchers showed that the difference in performance between seedlings growing in “maternal” soil and “non-maternal” soil was not the result of variations in soil nutrients or beneficial symbiotic relationships with fungi, thanks to lab work conducted at Yale by Camille Delavaux ’16 M.E.Sc., currently a doctoral student at the University of Kansas.

Using computer simulation models designed by Simon Stump, a postdoctoral associate at F&ES, the team then found that these pathogens can promote species coexistence and can lead to increased seed dispersal, which creates landscapes that allow pathogens to more effectively promote diversity.

“These results suggest that highly specialized pathogens are potentially an important, but largely overlooked driver of plant population and community dynamics,” said Comita. “Our findings underscore the importance of conserving both species and genetic diversity in tropical forests.”

Read the paper: Proceedings of the National Academy of Sciences

Article source: Yale School of Forestry & Environmental Studies (F&ES)

Image credit: Sean Mattson

Transcription Factor Network Gets to Heart of Wood Formation

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North Carolina State University researchers have uncovered how a complex network of transcription factors switch wood formation genes on and off. Understanding this transcriptional regulatory network has applications for modifying wood properties for timber, paper and biofuels, as well as making forest trees more disease- and pest-resistant.

“We’re building a complete story, so to speak, of how wood formation functions – all the intricate components, how they interact and how they fit together to regulate wood formation inside the cell walls of woody plants,” says Jack Wang, assistant professor in the College of Natural Resources and co-lead author of a Plant Cell article about the work.

Researchers with NC State’s Forest Biotechnology Group used transgenic black cottonwood (Populus trichocarpa), a species they’ve studied intensively, to identify interactions in a transcriptional regulatory network directed by a key transcription factor, PtrSND1-B1. The researchers documented four levels of interactions in the network, from DNA to enzyme levels. The work is an extension of two previous studies, in which functions of PtrSND1-B1 were discovered using a wood-forming cell system. These early studies were published in PNAS and Plant Cell by co-authors Quanzi Li, Ying-Chung Lin and Wei Li of the Forest Biotechnology Group, led by Vincent Chiang.

“Transcription factors – a complex network of them – regulate which wood formation genes are turned on or off,” Wang says. “Essentially these are high-level regulatory switches.

“Understanding this network allows us to identify single switches inside that complex network of transcription factors that could simultaneously control multiple wood-forming genes. Instead of working with one, two or three genes at a time, which is our current limit, plant biologists could work with tens of genes at a time.”

The new study upends ideas about transcriptional regulatory networks inferred from work with nonwoody species, such as Arabidopsis thaliana, a model plant.

“This network of transcription factor regulation in woody tissues is almost completely different from the regulatory processes in Arabidopsis and other plants,” says Hao Chen, co-lead author of the article and a postdoctoral researcher at NC State.

“Of 57 regulatory interactions we identified, 55 were specific to woody plant tissue, showing that herbaceous plants like Arabidopsis cannot stand in for woody plants.”

The study provides an extensive look at a transcriptional regulatory network in woody plants. Researchers’ goal is to provide a toolkit for building trees with specific properties needed for commercial timber, paper, biofuel production and conservation needs.

Plant biologists tested 42 of the interactions they found in lines of transgenic black cottonwood, verifying the function of about 90 percent. The network revealed which genes are common targets for specific transcription factors. As a result, researchers found nine new protein-protein interactions involved in forming lignin, a component in the cell wall that gives wood its strength and density.

Wang says several recent studies show that lignin is related to disease and insect resistance in trees, a major concern. A 2012 U.S. Forest Service report estimated that 7 percent of the nation’s forests are in jeopardy of losing more than a quarter of their tree vegetation by 2027. The amount of threatened vegetation rose by 40 percent in just six years.

“Studies like this that look at lignification and wood formation will have great value in helping to understand how trees can be made to be more robust and to improve forest health in general,” Wang says.

Read the paper: Plant Cell

Article source: North Carolina State University

Image credit: Jack P. Wang and Ilona Peszlen

Disappearing rice fields threaten more global warming

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All over China, a huge change has been taking place without any of us noticing. Rice paddies have been (and are being) converted at an astonishing rate into aquaculture ponds to produce more protein for the worlds growing populations. This change risks creating an unexpected impact on global warming.

International researchers, including Prof Chris Freeman from Bangor University, have found conversion of paddy fields to aquaculture is releasing massive amounts of the greenhouse gas methane into the atmosphere.

The UN Intergovernmental Panel on Climate Change (IPCC), have warned the planet will reach the crucial threshold of 1.5 degrees Celsius above pre-industrial levels by as early as 2030, precipitating the risk of extreme drought, wildfires, floods and food shortages for hundreds of millions of people. Freeman commented “Another source of methane is the last thing we need”.

It was always assumed that because rice paddies are already a huge source of atmospheric methane, nothing could happen to make a difficult situation worse.

When describing their work which appears in “Nature Climate Change”, Prof Chris Freeman commented: “We were amazed to discover that methane production from the converted rice paddies was massively higher than before conversion.”

Prof Freeman of the Bangor University‘s School of Natural Sciences explains:

“Paddy fields produce huge quantities of methane when decaying plant material is broken down by microbes called methanogens in the oxygen-free waterlogged paddy soils. But in the aquaculture ponds that are replacing the paddy fields, vast quantities of food are added to feed the crabs and fish that are being grown in them, and that massively increases the amount of rotting material for the methanogens to produce even more methane.”

Prof Freeman added: “We have known for some time that rice paddies were bad for global warming. But the realisation that there’s a “hidden” new source of problems is taking these threats to whole new level.”

There is also hope revealed in their studies though. Their research shows that if modifications were made to aerate the aquaculture ponds, much of the harmful methane could be eliminated before it reached the atmosphere. The IPCC warn global net emissions of carbon dioxide would need to fall by 45% from 2010 levels by 2030 and reach “net zero” around 2050 in order to keep the warming around 1.5 degrees C. The race is now on to ensure these changes are introduced before the current increasing rate of land use change exacerbates the global warming situation further.

Read the paper: Nature Climate Change

Article source: Bangor University

Image credit: CCO Public domain

Large and branched root systems can speed up growth of spruces

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According to a study by the Natural Resources Institute Finland (Luke), strong growth rate of spruces can be due to the structure of their root system. A large and branched root system offers a major benefit when competing for water and nutrients, and it can boost the growth of fast-growing spruces when compared to slow-growing ones already from the early stages.

The growth rate of trees varies: some trees grow slower and others faster by nature. The amount of nutrients and water a tree receives depends on its root system and the symbiotic mycorrhizal fungi growing in the root system. Earlier studies have determined that fast-growing spruce clones have more diverse selection of symbiotic fungi in their root systems. One cannot determine based on this result whether the diversity is the underlying reason for the fast growth rate or its consequence, however.

– Our goal was comparing the root systems of seedlings before the growth differences appear to find out whether small seedlings already show any external characteristics that anticipate good growth. We utilised Luke’s tree breeding data on the origins of fast- and slow-growing spruces, explains Taina Pennanen, Principal Scientist at Luke.

Fast-growing spruces grow extensive root systems already as seedlings

The 54 spruce seedlings that were included in the study were grown at a nursery garden and examined when they were 1.5 years of age and their sprouts were of the same height. Even though there were no differences in the height of the sprouts or the weight of the roots, the structures of the fast- and slow-growing spruces’ root systems were already clearly different

– Interestingly enough, there were more branches in the root systems of the fast-growing seedlings than in those of the slow-growing ones. There were more root tips than in the slow-growing seedlings and more lateral branches farther away from the base of the seedling than in the slow-growing seedlings, and the total length of the lateral branches was higher, explains Leena Hamberg, a Senior Scientist at Luke.

The large number of root tips farther away from the base of the seedling may allow the fast-growing seedlings to obtain, over the course of time, more diverse fungal contacts and more nutrients from the forest soil where neither nutrients nor fungi are evenly spread. This also enables good nutrient and water carrying capacity.

– Trees are highly long-lived plants, and the differences in the structural characteristics of the roots may become even more pronounced over time. We already know based on our previous studies that the characteristics of the roots of a spruce are hereditary. This phenomenon may, in part, explain the different growth rates of spruces, Taina Pennanen says.

Read the paper: Tree Physiology

Article source: Natural Resources Institute Finland (Luke)

Image credit: CCO Public domain

Drying without dying: how resurrection plants survive without water

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Aquaphotomics sheds light on how plants control their water structure to survive.

A small group of plants known as “resurrection plants” can survive months or even years without water. The research team of Kobe University’s Graduate School of Agricultural Science, led by Professor Dr Roumiana Tsenkova, in collaboration with a research group from Agrobioinstitute in Sofia, Bulgaria led by Professor Dr Dimitar Djilianov, made a significant step forward in understanding how they do it.

Using a pioneering aquaphotomics approach and completely non-destructive way of monitoring, the entire processes of drying and subsequent rehydration of one such plant – Haberlea rhodopensis – were compared to the same processes for its non-resurrection relative. The results showed that during drying, the resurrection plant performs fine restructuring of water in its leaves, preparing itself for the dry period by accumulating water molecular dimers and water molecules with 4 hydrogen bonds, while drastically diminishing free water molecules. This regulation of water structure is thought to be the mechanism of how the plant preserves its tissues against dehydration-induced damages, and allows it to survive in the dry state. The discovery that water structure is important for preservation of the plants during drought stress opens up a new direction for bioengineering and improving the drought tolerance ability of plants.

The research article was published in the online edition of Scientific Reports.

Life and water are intrinsically tied together. And yet, among living creatures there are some organisms able to survive long periods without water. They are called anhydrobiotic organisms. Among these, a small group of plants known as “resurrection plants” can survive long periods with almost completely desiccated vegetative tissues and recover fast and fully when water is available again. Enormous progress has been made recently at various levels to shed light on the mechanisms behind desiccation tolerance of resurrection plants. Understanding this phenomenon may help us use targeted genetic modifications to produce crop plants able to tolerate dehydration and adapt better to climate changes, in addition to better understanding of the role of water in life.

It is well established that resurrection plants have an array of adaptions and mechanisms which help them cope with the effects of dehydration – all the efforts of these adaptations are directed toward protecting the integrity of cellular structures and protection against oxidative stress. Little or no attention was paid so far to the role of water, as a partner during desiccation and recovery after severe stress. And yet all these organisms, despite producing different protective compounds, have one thing in common – water. Water in living organisms is a complex molecular matrix made of a defined number of different water molecular structures which are constantly being shaped by other components (biomolecules) and environmental influences.

In this research, Professor Dr Roumiana Tsenkova and Professor Dr Djilianov’s teams studied one of the resurrection plants – called Haberlea rhodopensis. This plant, together with around only 350 plant species on Earth, has an ability to survive very long periods of extreme dehydration, and then quickly, just hours after rewatering, it miraculously recovers to its fully functional, normal, living state.

Using near infrared light, in a completely non-destructive way, they monitored the processes of desiccation and rehydration of Haberlea rhodopensis plant and its relative non-resurrection plant species Deinostigma eberhardtii.

Near infrared spectroscopy and the novel “Aquaphotomics” approach developed by Prof. Tsenkova provided insight into the structural changes of water molecules in leaves of the plants and how they change during dehydration and rehydration. And for the first time it was observed that the water structure in the two plants, which are botanically very similar, in fact is drastically different.

The simple measurements of water content of the leaves revealed that Haberlea rhodopensis readily and very quickly reduces the water content to only 13%, as if it knows that it can survive without it. Deinostigma eberhardtii, on the other hand, tried hard throughout the dehydration to keep the water up until the point when it finally lost the battle (which is around 35% of water content, after which it cannot recover). However, when the structure of water molecules was examined during dehydration, it showed marked differences between the plants.

When Haberlea rhodopensis was losing water, it kept the number of certain water molecular species – free water molecules, water dimers, trimers and more hydrogen bonded water molecules – in the same ratios. While the numbers of these molecules diminished, their relationship was kept constant, suggesting orchestrated efforts by the plant to keep the water in a certain state. Such ability was not observed in Deinostigma eberhardtii, and the ratios of water species in the leaves randomly fluctuated.

Drastic differences of the water structure in the leaves were observed when both plants were in the completely dried state. In this final phase, Haberlea rhodopensis radically diminished free water molecules which are very important for all metabolic processes, and accumulated water dimers and water molecules with 4 hydrogen bonds. Deinostigma eberhardtii, in contrast never showed any such radical transformation of water structure. Up to the very last moment, even in the completely dried state it still had a lot of free water molecules, but now involved in spoliation and decay processes.

During rehydration, Haberlea rhodopensis showed the same orchestrated dynamics of reorganization of water structure, by performing orderly incremental changes of mostly all water species.

This research showed for the first time that the structure of water, not its content, is what matters to the survival of the organism. When people think about life, we often associate dynamic features with the processes in living systems. And yet, in this peculiar plant, in the absence of visible signs of ongoing metabolism, achieving a specific water structure was its survival tool.

As a result, the study performed by Prof. Tsenkova sheds some light on what may be the most fundamental feature of a living system – it is the structural organization, rather than the dynamics, that is at its core. And the structure of water is shaped by the numerous substances produced in the cells. These may be sugars, amino acids, or other biomolecules, but their final goal is achievement of a certain state of water molecular structure which allows the preservation of tissues and prevention of damage.

Future perspectives

This pioneering research adds to our growing understanding of the mechanisms by which some organisms achieve their remarkable tolerance to extreme dehydration. It discovered a novel target for modification in order to achieve better tolerance to drought in plants, which obviously can be achieved using different strategies (sugars, amino acids, proteins etc.) as long as they exert such influence on water molecular structure that would lead to decrease of free water molecules and increase of hydrogen bonded water. The aquaphotomics near infrared spectroscopy method allows direct, non-destructive insight into the living processes and water structure and dynamics in real time and is as a valuable new tool for studying not only the abiotic and biotic stress in plants, but many other phenomena in living systems.

Read the paper: Scientific Reports

Article source: Kobe University

Image credit: Wikimedia

How the humble marigold outsmarts a devastating tomato pest

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Scientists have revealed for the first time the natural weapon used by marigolds to protect tomato plants against destructive whiteflies.

Researchers from Newcastle University’s School of Natural and Environmental Sciences, carried out a study to prove what gardeners around the world have known for generations – marigolds repel tomato whiteflies.

Publishing their findings in the journal PLOS ONE, the experts have identified limonene – released by marigolds – as the main component responsible for keeping tomato whiteflies at bay. The insects find the smell of limonene repellent and are slowed down by the powerful chemical.

Large-scale application

The findings of the study have the potential to pave the way to developing a safer and cheaper alternatives to pesticides.

Since limonene repels the whitefly without killing them, using the chemical shouldn’t lead to resistance, and the study has shown that it doesn’t affect the quality of the produce. All it takes to deter the whiteflies is interspersing marigolds in tomato plots, or hang little pots of limonene in among the tomato plants so that the smell can disperse out into the tomato foliage.

In fact, the research team, led by Dr Colin Tosh and Niall Conboy, has shown that may be possible in to develop a product, similar to an air freshener, containing pure limonene, than can be hung in glasshouses to confuse the whiteflies by exposing them to a blast of limonene.

Newcastle University PhD student Niall said: “We spoke to many gardeners who knew marigolds were effective in protecting tomatoes against whiteflies, but it has never been tested scientifically.

“We found that the chemical which was released in the highest abundance from marigolds was limonene. This is exciting because limonene is inexpensive, it’s not harmful and it’s a lot less risky to use than pesticides, particularly when you don’t apply it to the crop and it is only a weak scent in the air.

“Most pesticides are sprayed onto the crops. This doesn’t only kill the pest that is targeted, it kills absolutely everything, including the natural enemies of the pest.”

Limonene makes up around 90% of the oil in citrus peel and is commonly found in household air fresheners and mosquito repellent.

Dr Tosh said: “There is great potential to use limonene indoors and outdoors, either by planting marigolds near tomatoes, or by using pods of pure limonene. Another important benefit of using limonene is that it’s not only safe to bees, but the marigolds provide nectar for the bees which are vital for pollination.

“Any alternative methods of whitefly control that can reduce pesticide use and introduce greater plant and animal diversity into agricultural and horticultural systems should be welcomed.”

The researchers carried out two big glasshouse trials. Working with French marigolds in the first experiment, they established that the repellent effect works and that marigolds are an effective companion plant to keep whiteflies away from the tomato plants.

For the second experiment, the team used a machine that allowed them to analyse the gaseous and volatile chemicals released by the plants. Through this they were able to pinpoint which chemical was released from the marigolds. They also determined that interspersing marigolds with other companion plants, that whiteflies don’t like, doesn’t increase or decrease the repellent effect. It means that non-host plants of the whiteflies can repel them, not just marigolds.

A notorious pest

Whitefly adults are tiny, moth-like insects that feed on plant sap. They cause severe produce losses to an array of crops through transmission of a number of plant viruses and encouraging mould growth on the plant.

Dr Tosh said: “Direct feeding from both adults and larvae results in honeydew secretion at a very high rate. Honeydew secretion that covers the leaves reduces the photosynthetic capacity of the plant and renders fruit unmarketable.”

Further studies will focus on developing a three companion plant mixture that will repel three major insect pests of tomato – whiteflies, spider mites and thrips.

Longer term, the researchers aim to publish a guide focussing on companion plants as an alternative to pesticides, which would be suitable across range of horticultural problems.

Read the paper: PLOS ONE

Article source:Newcastle University

Image credit: CCO Public domain

Decades of Tree Rings Extend Today’s High-Tech Climate Stories

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Satellite imagery, carbon dioxide measurements, and computer models all help scientists understand how climate and carbon dynamics are changing in the world’s forests. But the technology powering these high-tech data only stretches back about thirty years, limiting our picture of long-term change.

A new study in Nature Communications co-authored by HF Senior Ecologist Neil Pederson with scientists from Columbia University, ETH Zürich, and elsewhere shows how information revealed by a new method of analyzing tree rings matches the story told by more high-tech equipment over the short-term. Because trees are long-lived, looking back in their rings with this new approach may add decades or even centuries to our understanding of carbon storage and climate change in forests.

To test whether tree rings are a good proxy for satellite and other data, the scientists examined ring samples from two widespread tree species — tulip poplar (Liriodendron tulipifera) and northern red oak (Quercus rubra) – growing in three climatically different regions of the eastern US.

By analyzing the carbon and oxygen molecules (stable isotopes) stored in the rings, they could compare the trees’ own picture of forest productivity to estimates derived from satellites. They found strong agreement each year, and over time.

The tree rings also revealed that the biggest changes in annual forest growth were linked to moisture availability, regardless of climate. “Our method showed that the productivity of a forest can be estimated using information from just five trees,” says Laia Andreu Hayles, an Associate Research Professor at the Tree-Ring Laboratory of Columbia University‘s Lamont-Doherty Earth Observatory, and co-author of the new study. “The stable isotopes measured in tree rings are highly sensitive to tracking moisture.”

The team says the full power of this new method would rely on an expanded network of tree ring research. “When we put tree ring data to work in historical climate models, we find that the models are more powerful when more species are included,” says Neil Pederson with scientists from Columbia University,, Harvard Forest Senior Ecologist. “I suspect this might also be the case when we use models to look forward, to future forest productivity and carbon storage.”

Read the paper: Nature Communications

Article source:Harvard University

Image credit: CCO Public domain

Living together: how legume roots accommodate two distinct microbial partners

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A research team including University of Tsukuba identifies a gene that controls how legume roots form biological partnerships with two completely different types of microbe—bacteria and fungi—that both help supply nutrients

Legumes such as peas and beans form intimate and mutually beneficial partnerships (symbioses) with nitrogen-fixing bacteria, rhizobia. The plant benefits from an enhanced supply of nitrogen, ‘fixed’ from the air by the rhizobia, while the bacteria benefit from protective accommodation inside special structures, called root nodules, that supply nutrients from the host plant. A different type of symbiosis is formed between the roots of many plant species and soil fungi, called mycorrhizal fungi. Both types of complex plant–microbe interactions are crucial for supplying plants with nutrients, but many details of how these symbioses develop remain unclear.

University of Tsukuba researchers, collaborating with two other Japanese universities, have revealed a key piece in the jigsaw puzzle of mechanisms that control the developmental processes behind the symbioses of roots with microbes. The team identified a gene that is pivotal in controlling how legume roots establish cellular accommodation for rhizobia bacteria, described in a recent publication in PLoS Genetics.

When the gene is inactivated in a mutant plant, the roots produce dramatically fewer nitrogen-fixing nodules because the usual (intracellular) route of entry for the bacteria, called an infection thread, does not develop properly in the root cells. However, small numbers of nodules do develop, some weeks later than normal, when the bacteria enter by a different (intercellular) route between the root cells.

The team named the gene lack of symbiont accommodation (lan). They showed it is inactivated in the mutant, and found it is closely related to a gene in other plant species. It is thought to encode a protein that acts in a complex of other regulatory proteins (called Mediator) to control the expression of numerous genes and processes. This is the first report of the gene’s involvement in controlling plant–microbe interactions.

“We used the model legume Lotus japonicus, which grows and reproduces rapidly and has a smaller, simpler genome than most crop plants,” says corresponding author Takuya Suzaki. “Our research methods included genetic modification, studying the plant’s anatomy by microscopy using fluorescent dyes, genome sequencing, and producing mutant plants using the latest gene editing technologies.”

The lan gene is important not only for symbiosis with rhizobia: the team showed that the gene is also required for establishing symbioses with mycorrhizal fungi.

“This study shows that a single control system operates in establishing two completely different symbioses that are important for plant nutrition,” says Suzaki. “Our results have wider implications for understanding how plant developmental processes are coordinated.”

Read the paper: PLoS Genetics

Article source: University of Tsukuba

Image credit: Sui-setz

Research identifies mechanism that helps plants fight bacterial infection

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A team led by a plant pathologist at the University of California, Riverside, has identified a regulatory, genetic mechanism in plants that could help fight bacterial infection.

“By better understanding this molecular mechanism of regulation, we can modify or treat crops to induce their immune response against bacterial pathogens,” said Hailing Jin, a professor of microbiology and plant pathology, who led the research.

Working on Arabidopsis thaliana, a small flowering plant widely used by biologists as a model species, Jin’s research team found that Argonaute protein, a major core protein in the RNA interference machinery, is controlled by a process called “post-translational modification” during bacterial infection.

This process controls the level of the Argonaute protein and its associated small RNAs — molecules that regulate biological processes by interfering with gene expression. This provides double security in regulating the RNA interference machinery. RNA interference, or RNAi, is an important cellular mechanism that many organisms use to regulate gene expression. It involves turning off genes, also known as “gene silencing.”

A previous study in Jin’s lab identified that one of 10 Argonaute proteins in Arabidopsis is induced by bacterial infection and contributes to plant immunity — the higher the level of the protein, the higher the plant immunity. A high level of the protein, however, can limit the plant’s growth.

Under normal plant growth conditions, the Argonaute protein and its associated small RNAs are well controlled by arginine methylation – a type of post-translational modification of the Argonaute protein. This regulates the Argonaute protein and prevents it from accumulating to high levels. The small RNAs associated with the Argonaute protein are also prevented from accumulating to higher levels, allowing the plant to save energy for growth.

During bacterial infection, however, arginine methylation of the Argonaute protein is suppressed, which leads to the accumulation of the Argonaute protein and its associated small RNAs that contribute to plant immunity. Together, these two changes allow the plant to both survive and defend itself.

“If the Argonaute protein and the associated small RNAs were to remain at such high levels after normal conditions returned, it would be detrimental to plant growth,” Jin said. “But post-translational modification of the Argonaute protein, restored under normal conditions, decreases these levels to promote plant growth.”

Study results appear in Nature Communications.

Jin explained that all plants possess the RNAi machinery, as well as the equivalent plant-immunity-related Argonaute protein. RNA silencing is seen in all mammals, plants, and most eukaryotes.

“Until our study, how the Argonaute protein got controlled during a pathogen attack was unclear, and just how plants’ immune responses got regulated by the RNAi machinery was largely a mystery,” said Jin, who holds the Cy Mouradick Endowed Chair at UCR and is a member of UCR’s Institute for Integrative Genome Biology. “Ours is the first study to show that post-translational modification regulates the RNAi machinery in plant immune responses.”

Jin was joined in the study by UCR’s Po Hu, Hongwei Zhao, Pei Zhu, Yongsheng Xiao, Weili Miao, and Yinsheng Wang.

Read the paper: Nature Communications

Article source:University of California – Riverside

Image credit: Alexey Kuzmin in Pixabay

How Capsella followed its lonely heart

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The Brassicaceae plant family boasts a stunning diversity of fruit shapes. But even in this cosmopolitan company the heart-shaped seed pods of the Capsella genus stand out.

An estimated 8 million years ago Capsella embarked on a different evolutionary pathway from its close relatives Arabidopsis and Camelina.

This led to radically different shapes in the fruits which in these plants form pods that enclose the seeds prior to dispersal or dehiscence. Arabidopsis fruits are cylindrical, Camelina’s are spherical, while Capsella conspicuously follows its own heart.

Most of the diversity in the Brassicaceae occurs in one part of the fruit called the valves or seed pod walls. But until now it was not clear which mechanisms lay behind these differences.

Research, published in the journal Current Biology uncovers key processes involved in this genetic journey and offers evidence as to how and why these shapes occur.

The team from the John Innes Centre used gene-editing technology, transgenic plants and molecular reporting techniques to show that a well characterised gene called INDEHISCENT (IND) lay at the heart of the matter.

In the model plant Arabidopsis, this gene is locally expressed only in strips of cells that regulate seed dispersal or pod shatter.

In Capsella, experiments here show that IND has expanded its local expression into the upper part of the valves, the shoulders that give the plant its characteristic heart shaped fruits. Gene-edited mutant lines without the IND gene showed significantly reduced shoulders compared to the wild type.

Previous studies showed that IND regulates the plant growth hormone auxin. Here the team used two reporter genes with fluorescent tags which highlighted distinct spots or maxima of auxin at the twin shoulders of Capsella’s heart-shaped pods. However, these maxima were absent in plants without IND activity.

“So, we can say clearly that IND is important for the Capsella fruit shape and it mediates its effects by directly upregulating auxin biosynthesis in these pods to pilot growth towards these peaks,” explains Prof Lars Ostergaard of the John Innes Centre, an author on the study.

“That is what makes this study so exciting. Not only have we found out that IND has at least a partial role in creating the shape, but we have also found out what the gene does in the tissue that allows this shape to form,” he adds.

But why have these mysterious shapes evolved over the past 8 million years?

“Of the carbons and sugars that are produced in the pod from captured sunlight during photosynthesis about 50 per cent go into growing the seeds. So, we could imagine an evolutionary edge for Capsella due the its larger, flatter shape,” says Professor Ostergaard.

The Brassicaceae family includes a host of economically important domestic crops such as oilseed rape and it is possible that these latest findings in Capsella could find expression in commercial crops of tomorrow:

“By using this fundamental knowledge and translating it into the commercial crop we may be able to create a denser oilseed rape canopy with a bigger pod surface area so that seeds grow bigger and yields increase,” says Professor Ostergaard.

The findings support a growing number of studies in developmental biology which show that changes in regulatory DNA sequence in key controlling genes such as IND can lead to diverse expression patterns responsible for changes in organ shape both in natural evolution and in the domestication of crops.

Read the paper: Current Biology

Article source:John Innes Centre

Image credit: Andrew Davis